Electromagnetic actuator mounting structure

ABSTRACT

An improved electromagnetic actuator having a coil ( 10 ) on which a current is impressed, a magnet ( 20 ) that forms a magnetic circuit across a magnetic gap (G) with a magnet yoke ( 21 ), and having a diaphragm ( 11 ) that vibrates when a high-frequency current is impressed, and a vibration plate ( 22 ) that vibrates when a low-frequency current is impressed, with these parts enclosed within a basket ( 3 ) and the coil ( 10 ) placed within the magnetic gap (G). As one invention, a radial array of magnets, a vibration plate with a doublesuspension structure, and a bottom plate of magnetic shielding material are placed in the basket to suppress the leakage of magnetic flux. As an invention to further improve the frequency characteristics by means of the mounting structure of the electromagnetic actuator, elastic packing ( 5, 7 ) is sandwiched between the basket of the electromagnetic actuator and the housing case of the portable electronic equipment, and also between the basket of the electromagnetic actuator and the mounting.

FIELD OF TECHNOLOGY TO WHICH INVENTION BELONGS

[0001] This invention concerns an electromagnetic actuator and astructure for mounting it in portable electronic equipment such as apager or portable telephone, as a means of notification of a call bymeans of a buzzer, audio tone or vibration when a signal is received.

BACKGROUND OF INVENTION

[0002] Pagers and portable telephones are made with built-innotification devices, which have vibrators as well as buzzers, as ameans of call notification in conferences and other locations where itis inappropriate to use an audible alarm. If the vibration mode isswitched on in advance, the vibrator is driven instead of an alarm beingsounded when a call comes in, and the recipient is made aware of thecall by means of the vibration.

[0003] In the past, this vibration has been created by a small motor, aneccentric weight attached to the shaft of the motor such that avibration it generated when the battery-driven motor is caused torotate.

[0004] As portable electronic equipment including pagers and portabletelephones has become smaller and lighter, further miniaturization ofmotors has become necessary, but there are limits to the miniaturizationof call notification devices with both vibrators and buzzers. Moreover,because the amount of vibration from battery drive is fixed, there is afurther drawback in that there are individual differences in thestrength of vibration necessary.

[0005] To resolve this problem, the applicants have developed aspeaker-type electromagnetic actuator that does not use the small motorof U.S. patent No. 5,528,697.

[0006] This electromagnetic actuator is an epochal product that combinesthe function of selecting the vibration ring, buzzer ring or tone ringas a vibration mode into the same unit as the speaker function. It is soconstituted that when a given frequency is impressed on a coil, theinteraction of the magnetic field of the magnets and the currentimpressed on the coil generates vibration in a vibration plate in thecase of a low frequency or a resonant tone in a diaphragm in the case ofa high frequency. Moreover, because it is possible to control the amountof vibration and the frequency, the amount of vibration can be adjustedand set at the level desired by the individual.

[0007] As portable telephone equipment has become widely used, there hasbeen demand for an electromagnetic actuator that can suppress theexternal leakage of magnetic flux and also have good frequencycharacteristics even though small in size. There has also been demandfor high durability within the usage environment of portable electronicequipment with internal electromagnetic actuators, such that they do notbreak even if the user drops them. There is further demand, from theperspective of cost reduction, for reduction of the number of parts andfor ease of assembly.

OVERVIEW OF INVENTION

[0008] This invention is an improved electromagnetic actuator with asmall and simple structure, having a coil on which current is impressed,a magnet that forms a magnetic circuit between its poles across amagnetic gap with a magnet yoke, and having a diaphragm that vibrateswhen a high-frequency current is impressed, and a vibration plate thatvibrates when a low-frequency current is impressed, with the coil placedwithin the magnetic gap and the parts enclosed within a basket. Thestructure for mounting the electromagnetic actuator is also improved.

[0009] One purpose of this invention is to suppress the external leakageof magnetic flux. To achieve this purpose, this invention can beconstituted with a radial array of magnets, a vibration plate with adouble-suspension structure, and a bottom plate of magnetic shieldingmaterial placed in the basket.

[0010] Another purpose of this invention is to constitute theelectromagnetic actuator with good frequency characteristics even whenit is small. To achieve that purpose, this invention selects thematerial of the vibration plate and also uses the basket as a thirdvibrator, in addition to the diaphragm and the vibration plate.

[0011] A further purpose of this invention is to constitute anelectromagnetic actuator with high impact resistance. To achieve thispurpose, the invention is constituted with a elastic material thatretains and supports the vibration plate within the basket.

[0012] This invention also has the purpose of cost-reduction, and isconstituted with a diaphragm that holds the coil in a raised portion,and a vibration plate that holds both the magnets and the magnet yoke onits surface.

[0013] In addition, this invention has the purpose of further improvingfrequency characteristics and impact resistance by means of the mountingstructure for the electromagnetic actuator. Thus this invention isconstituted with elastic packing sandwiched between the basket of theelectromagnetic actuator and the housing case of the portable electronicequipment, and also between the basket of the electromagnetic actuatorand the mounting structure.

BRIEF EXPLANATION OF DRAWINGS

[0014]FIG. 1 is a cross section showing the assembly structure of theelectromagnetic actuator of this invention.

[0015]FIG. 2 is an exploded oblique drawing of the first vibrator, whichis a structural part of the electromagnetic actuator of this invention.

[0016]FIG. 3 is an exploded oblique drawing of the second vibrator,which is a structural part of the electromagnetic actuator of thisinvention.

[0017]FIG. 4 is an exploded oblique drawing of the basket, which is astructural part of the electromagnetic actuator of this invention.

[0018]FIG. 5 is an explanatory drawing showing the order of assembly ofthe electromagnetic actuator of this invention.

[0019]FIG. 6 is an explanatory drawing showing a partial cross sectionof the equipment case and mounting substrate as the mounting structureof the electromagnetic actuator of this invention.

[0020]FIG. 7 is an oblique drawing showing the elastic packing used inthe mounting structure of the electromagnetic actuator of FIG. 6.

[0021]FIG. 8 is a graph showing the frequency characteristics of themounting structure of the electromagnetic actuator without the elasticpacking of FIG. 7.

[0022]FIG. 8 is a graph showing the frequency characteristics of themounting structure of the electromagnetic actuator with the elasticpacking of FIG. 7.

DETAILED EXPLANATION

[0023] To explain this invention in detail with reference to thedrawings, the electromagnetic actuator of this invention is constituted,as shown in FIG. 1, with a first vibrator 1 that produces a resonanttone when a high frequency current is impressed, a second vibrator 2that produces a vibration when a low frequency current is impressed, anda basket 3 that contains the first and second vibrators 1, 2 as theminimum necessary assembly parts.

[0024] The first vibrator 1 comprises, as shown in FIG. 2, a voice coil(hereafter simply “coil”)10 that is wound in a circular shape and onwhich either a high frequency or low frequency current can be impressed,and a thin diaphragm 11 that holds the coil 10 in place.

[0025] The diaphragm 11 is formed from a thin disk of a polymer materialsuch as polyether imide (PEI). This diaphragm 11 has a concentriccircular projection 11 a that projects to a given height from thesurface to hold the coil 10 in place. The surface of the diaphragm 11also has a concentric circular lip 11 d near the outer edge that dividesthe vibrating portion 11 d from the outer rim 11 c that is necessary forassembly with the basket 3. The coil 10 is fixed to the projection 11 aon the surface of the diaphragm 11, and is thus held in place by thediaphragm 11.

[0026] Because of the structure of the first vibrator 1, no othersupport member is needed to hold the coil 10 in place, and so it ispossible to reduce the number of parts and also to mount the coil 10easily. Moreover, because the coil 10 is fixed to the projection 11 athat projects from the surface of the vibrating portion I la, it ispossible for this vibrating portion 11 b to maintain good frequencycharacteristics, unaffected by having the coil 10 mounted.

[0027] The second vibrator 2 comprises, as shown in FIG. 3, a magnet 20that forms a magnetic circuit, a magnet yoke 21 that holds the magnet 20in place, and a thin vibrator plate 22 that holds the magnet yoke 21 inplace.

[0028] The magnet 20 is shaped for a radial array. The magnet 20 of thisradial array forms a ring with its north and south poles on the innerand outer peripheries to produce a magnetic circuit radiating betweenpoles. The magnet is held within the magnet yoke 21 and forms a unitwith the magnet yoke 21 such that the north and south poles arepositioned parallel to the first vibrator 1 and second vibrator 2. Themagnet 20 is divided into four or some other number of pieces tofacilitate placement in the magnet yoke 21.

[0029] The magnet yoke 21 is saucer shaped, with an outer rim 21 a, anda raised pole piece 21 b in the center. This pole piece 21 b is a raisedportion with a diameter smaller than the inner periphery of the magnet20, so as to interpose a magnetic gap G (see FIG. 1) in the innerperiphery of the magnet 20.

[0030] The vibration plate 22 is punched from a sheet of springy metal,and has s springy structure with a center plate 22 a that is fixed tothe magnet yoke 21, an outer rim 22 b that can be fixed to the basket 3,and multiple curved arms 22 c that connect the center plate and theouter rim.

[0031] Because the second vibrator 2 has the radially arrayed magnet 20,it is possible to suppress the leakage of magnetic flux in the directionof vibration of the diaphragm 11 and vibration plate 22 that vibratethrough the attraction and repulsion by the magnetic force of the magnet20 and the magnetic force generated by the coil 10. As with theconstitution of the first vibrator 1, there is no need for a separatesupport member to support the magnet yoke 21, and so it is possible toreduce the number of parts and to assemble the magnet 20 and the magnetyoke 21 easily.

[0032] Now, to assure space for the coil 10 to enter to the back of themagnetic gap G in the magnet yoke 21, the yoke is assembled with aspacer 24 between it and the magnet 20.

[0033] The second vibrator 2 has, in addition to the vibration plate 22described above, another vibration plate 23 with a center plate 23 a, anouter rim 23 b that can be fixed to the basket 3, and multiple curvedarms 23 c that connect the center plate and the outer rim. The centerhole 23 d of the vibration plate 23 has a diameter larger than the outerperiphery of the coil 11 so that the coil 10 can be placed within themagnetic gap G.

[0034] Because the second vibrator 2 has two vibration plates 23 thatform a double-suspension structure, the magnetic shielding is furtherenhanced and it is possible to suppress the leakage of magnetic fluxeven more effectively. And because it improves the vibration resistance,it is possible to maintain the initial vibration characteristics.

[0035] The vibration plates 22, 23 can be made of any stainless steel oralloy of copper and titanium that does not require an aging/hardeningprocess after being a punched. In order to improve the hardness/Young'smodulus of the spring parts of vibration plates of these materials, itis possible to increase the resonant frequency to produce a large amountof vibration. Now, multiple notches 22 d, 23 e are made at regularintervals in the outer rims 22 b, s2 b in order to fix these vibrationplates 22, 23 inside the basket 3.

[0036] As shown in FIG. 4, the basket 3 is formed as a low round housingthat comprises a basket body 30 that accommodates the first and secondvibrators 1, 2, a cover plate 31 that covers the upper side of thebasket body 30, and a thin, flat bottom plate 32 that covers the bottomside of the basket body 30.

[0037] The basket body 30 is a round frame made of a polymer materialsuch as polybutylene terephthalate (PBT). Its inner surface has steps 30a to receive the outer rim 11 c of the diaphragm 11, as well as thecover plate 31. The lower side of the steps 30 projections 30 b (onlyone is shown in FIG. 4) that engage the notches 22 d, 23 e of thevibration plates 22, 23. The basket body 30 also has air holes 30 c inits side, and on the upper edge there is a cutout 30 d for the flexisubstrate that makes the electrical connection with the coil 10. Thecover plate 31 is disk-shaped, and has a number of sound holes 31 a, 31b . . . This cover plate 31 can be made of a metal with magneticproperties so as to function as a magnetic shield.

[0038] The bottom plate 32 is a part of the basket 3, and is formed of apolymer-polyethylene— terephthalate (PET), polyether imide (PEI) orpolyimide (PI)— so as to function as a thin vibration plate. It is bestformed with a thickness not less than 50 μm and not greater than 100 μm.

[0039] When this bottom plate 32 is provided, it becomes a thirdvibrator of the electromagnetic actuator, and improves the frequencycharacteristics, including those of the first vibrator 1 and the secondvibrator 2. Moreover, it is good to have at least one concentric lip 32a and or 32 b on its surface; the lips 32 a, 32 b can improveefficiently the frequency characteristics of the bottom plate 32.

[0040] Within the basket 3 there is an elastic piece 33 formed of arubber-based elastomer. This elastic piece 33 comprises a cylindricalouter wall 33 a that fits against the inside of the basket body 30, anda protrusion 33 b that projects inward from the outer wall 33 a. Theprotrusion 33 b of the elastic piece 33 can be continuous around theinner circumference, or it can be divided into three or four sections.In the upper edge of the elastic piece 33 there are notches 33 c thatfit the projections 30 b of the basket body 30.

[0041] Aside from this elastic piece 33, the basket 3 has a spacer ring34 to assure vibration space between the vibration plate 22 of thesecond vibrator 2 and the bottom plate 32 of the basket 3.

[0042] Of the parts of the basket 3, as shown in FIG. 1, the outer rim22 b of the vibration plate 22 is sandwiched between the elastic piece33 and the spacer ring 34. In this way, the second vibrator 2 issupported, and the upper surface of the outer rim 23 b of the vibrationplate 23 is held down against the step 30 b of the basket body 30.

[0043] By providing this elastic piece 33 within the basket 3, it ispossible to buffer the impact force, in the event that the user dropsthe portable electronic equipment in which the electromagnetic actuatoris mounted, by directing it from the second vibrator 2 into the elasticpiece 33. Moreover, because the protrusion 33b is in contact with theouter edge of the magnet yoke 11, if the second vibrator 2 is shakensideways on impact, the protrusion 33 b acts as a stopper against theouter edge of the magnet yoke 11, thus preventing distortion of thevibration plates 23, 23. Therefore, it is possible to provide greatimpact resistance such that the electromagnetic actuator is not broken.

[0044] To assemble the actuator from the various parts described above,the basket body 30 is taken as the base and the diaphragm 11 with thecoil 10 attached, and then the cover plate 31 are fit in to the steps 30a through the top of the basket body 30. The terminals of the coil 10are kept long enough to allow the vibration of the diaphragm 11, and areconnected electrically to the flexi substrate 4 that projects outwardfrom the outer rim of the diaphragm 11.

[0045] From the under side of the basket body 30, on the other hand, theupper vibration plate 23 of the second vibrator 2 is inserted with theprojections 30 b of the basket body 30 aligned with the notches 23 e. Inthe same way, the elastic piece 33 is inserted into the basket body 30with the projections 30 b of the basket body 30 aligned with the notches30 d, and assembled so that the outer rim 23 b of the upper vibrationplate 2 of the second vibrator 2 is supported. Next, the magnet yoke 21that supports the spacer 24 and the magnet 20 is attached to the surfaceof the lower vibration plate 22, and the lower vibration plate 22 isinserted into the basket body 30. A spacer ring 34 that presses theouter rim 22b of the lower vibration plate 22 against the elastic piece33 is inserted, and then the bottom plate 32 is fit into the loweropening of the basket body 30.

[0046] In the assembled actuator, the first vibrator 1 and the secondvibrator 2 are facing as shown in FIG. 1, and the coil 10, suspendedthrough the central opening 23 d of the upper vibration plate 23, is inposition to be attracted and repulsed upward and downward within themagnetic gap G between the inner circumference of the magnet 20 and thepole piece 21 b of the magnet yoke 21.

[0047] In this electromagnetic actuator, when the designated frequencyis impressed on the coil 10, the electromagnetic action between themagnetic field of the magnet 20 and the current impressed on the coil 10causes a vibration to be generated by the vibration plates 22, 23 at alow frequency, or a resonant tone to be generated by the vibration ofthe diaphragm at a high frequency. And because it is possible to controlthe amount of vibration and the frequency, the amount of vibration canbe adjusted to the individual preference.

[0048] When this electromagnetic actuator is mounted in portableelectronic equipment, the electromagnetic actuator is normally fixed inplace within the equipment case by positioning it so as to cover thesound holes in the equipment case, with a ring of elastic packingsandwiched between the equipment case and the basket of theelectromagnetic actuator.

[0049] The structure for attachment of the electromagnetic actuator ofthis invention is, as shown in FIG. 6, to position it over the soundholes B so that a ring-shaped elastic packing 5 is sandwiched betweenthe inside surface of the equipment case C and the basket 3 of theelectromagnetic actuator A. At the same time, the elastic packing 7 isheld between the basket 3 of the electromagnetic actuator A and thesurface of the mounting substrate 6 that accommodates theelectromagnetic actuator A within the equipment case C.

[0050] These elastic packings 5, 7 can be made of a polymer materialsuch as urethane foam. Of these, the elastic packing 7 that is placedagainst the surface of the mounting substrate 6 comprises a cylindricalouter wall 7 a and an elastic base 7 b that extends inward from theouter wall 7 a, as shown in FIG. 7.

[0051] This elastic packing 7 is prepared as a part of theelectromagnetic actuator A by fitting the outer wall 7 a to the lowercircumference of the basket body 30 as shown in FIG. 6, with the elasticbase 7 b against the surface of the mounting substrate 6 and sported bymultiple stops 6 a, 6 b located on the mounting substrate 6. In thisway, the elastic base 7 b is in place between the surface of themounting substrate 6 and the basket 3 of the electromagnetic actuator A,and the electromagnetic actuator A is accommodated within the equipmentcase C.

[0052] Now, at the bottom of the electromagnetic actuator A there is, asshown in FIG. 6, an opening 6 c in the mounting substrate 6. And asshown in FIG. 7, there can be notches 7 c in the elastic base 7 b thatgo through the outer wall 7 a to provide air passages.

[0053] Regarding the effect of this structure for mounting theelectromagnetic actuator, compared with the frequency shown in FIG. 8for the electromagnetic actuator mount without elastic backing, FIG. 9shows that better stability is available in frequency characteristics inthe range from 800 Hz to 3 Khz, and so this structure is capable ofimproving frequency characteristics even though it is a small and simplestructure.

[0054] The words and expressions used above in the particulars of thisinvention were chosen simply for the purpose of explanation, and do notlimit the content of the invention in any way. In the event thatlimiting words or expressions have been used, that is not intended toexclude equivalent modes of this invention or parts thereof. It isclear, therefore, that it is possible to make various changes to thescope of this invention for which rights are claimed.

What is claimed is:
 1. An electromagnetic actuator having a coil onwhich current is impressed, a magnet that forms a magnetic circuitbetween its poles across a magnetic gap with a magnet yoke, a diaphragmthat vibrates by magnetic action when a high-frequency current isimpressed and a vibration plate that vibrates by magnetic action when alow-frequency current is impressed, with the coil positioned within themagnetic gap and the parts thereof being accommodated in a basket, inwhich the magnet is held in a magnet yoke and the magnet yoke holdingthe magnet is supported by the surface of the vibration plate, and themagnet, magnet yoke and vibration plate are assembled in a single unit.2. An electromagnetic actuator mounting structure for mounting anelectromagnetic actuator inside portable electronic equipment in whichelastic packing is sandwiched between the inner surface of the equipmentcase and the basket of the electromagnetic actuator and between thebasket of the electromagnetic actuator and the electromagnetic actuatormounting substrate, so that the electromagnetic actuator is mountedinside the portable electronic equipment.
 3. An electromagnetic actuatormounting structure as described in claim 2 above, in which the elasticpacking is fitted to the bottom of the basket, and is sandwiched betweenthe basket of the electromagnetic actuator and the mounting substrate.